Raspberry Pi gets 'Turbo Mode' support

The Raspberry Pi can now run at speeds of up to 1GHz without losing its warranty, thanks to a cpufreq-driven 'Turbo Mode.'

The Raspberry Pi Foundation has announced a new feature for its low-cost credit-card-sized ARM-powered microcomputer: overclocking up to 1GHz without voiding the warranty.

The Broadcom BCM2835 system-on-chip (SoC) processor found at the heart of the Raspberry Pi was originally designed for use in multimedia-centric applications like set-top boxes and smart TVs. The result is a design which pairs a massively powerful graphics processor with a relatively weedy CPU based on the outdated ARMv6 instruction set architecture.

To boost the Pi's performance in general-purpose computing tasks, some users choose to edit the config.txt file found on the Pi's SD card to boost the clockspeed above the stock 700MHz. The result, as our own testing proved, is a near-linear improvement in CPU-based performance - but one that is limited by the capabilities of the SoC itself.

During testing, we were able to get our Raspberry Pi to 900MHz, after which it would fail to boot. The config.txt file, which replaces the CMOS setup of a desktop or laptop PC, provides a helpful tool for fixing this: overvolting. Trouble is, increasing the voltage sets a 'sticky bit' in the processor and renders the warranty null and void.

At least, it used to. In efforts to appease those who find the performance of the sub-£30 Raspberry Pi disappointing, the Foundation has announced Turbo Mode - a software-driven dynamic overclocking system which includes integral overvoltage support without sacrificing the warranty.

Putting the SoC's performance under the control of the cpufreq driver - the same Linux daemon that provides control over dynamic clock speed on processors from Intel and AMD - the Turbo Mode, unlike editing config.txt, is able to modify the speed of the processor on the fly and includes safety valves like clocking the processor back down again should temperatures raise above the safe point of 85°C and only overvolting and overclocking when the system is under load.

The Turbo Mode is accessible using the raspi-config tool on the latest Raspbian Debian variant, and provides access to five pre-set overclocking modes. The highest of these increase the clock speed of the processor to 1GHz under load - something we were unable to achieve without overvolting - and combines with other performance-boosting tweaks to offer around 50 per cent better performance on CPU-driven tasks than the stock 700MHz clockspeed.

Additional changes to the Raspbian Linux distribution add out-of-the-box support for Wi-Fi dongles based on the RTL8188CUS chipset, boosted analogue audio quality and some additional software, along with a bugfixed USB driver that boosts overall system performance by around 10 per cent without overclocking.

Full details of the changes can be found on the official website. Sadly, there is still no news yet of accelerated graphics support for the GUI - one of the biggest performance-sappers for general-purpose usage.

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17 Comments

I just got the USB cord for my Pi last night. It's pretty good but browsing the internet can be a bit slow with the CPU is loaded at 100% all the time just because you have two tabs open :(. I wasn't expecting a lot for $35 but it's still pretty sweet.

Originally Posted by The_BeastI just got the USB cord for my Pi last night. It's pretty good but browsing the internet can be a bit slow with the CPU is loaded at 100% all the time just because you have two tabs open :(. I wasn't expecting a lot for $35 but it's still pretty sweet.

That's due to the lack of accelerated X driver: all 2D graphics operations - including scrolling in a browser - go through the weedy CPU and not the beefy GPU. The result: a painful operating experience.

Turbo Mode will help by giving the system an overall speed tweak, but it won't be pleasant to use until (unless) an accelerated driver is provided.

Originally Posted by Gareth HalfacreeThat's due to the lack of accelerated X driver: all 2D graphics operations - including scrolling in a browser - go through the weedy CPU and not the beefy GPU. The result: a painful operating experience.

Turbo Mode will help by giving the system an overall speed tweak, but it won't be pleasant to use until (unless) an accelerated driver is provided.

I'm not complaining, I wasn't expecting much to begin with and web browsing isn't it's main purpose. It's just kinda slow setting it, but it's more because I'm not Linux savvy....yet :D

My warranty was already gone when I tried overvolting about a month ago :D. I still can't achieve much over 850MHz though... My power supply is a lot better than the last one I tried, but I still can't rule out the possibility that it might be struggling under load. The test points now read ~4.8v/4.9v, as opposed to ~4.6v with my last power supply, but that was measured at idle; I'll have to test it under load, I guess. I'll give this new firmware a shot first though. 1GHz is the goal, but if I can get to 900MHz stable then I'll be happy!

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Originally Posted by asuraShameless plug is shameless. Only you "forgot" to provide a link Mr. Halfacree.

Not quite; read the comment thread in the forums ;)

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Originally Posted by MSHunterSO 1080p with doulby surround should play fluid now?

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Originally Posted by PicarroI still want fullHD blu ray playback at 40mbps without stuttering. Please.

The only issues I've had with 1080p h.264 playback have been due to insufficient network bandwidth; in the case of seriously high bitrate stuff, I've had a regular PC fail to play video smoothly when using a 100mbit network adapter. I've not tried really high bitrate stuff on the Pi from a USB source however; most of my HD movies are compressed down to ~15GB, and they play just fine over the network.

The Pi can only use the CPU to decode audio, so anything at 5.1 or over will likely make the Pi struggle, even with an overclock. The solution is audio passthrough.

And bear in mind that it was never designed to be a $35 HTPC; the fact that the GPU can handle 1080p video is purely a bonus.

Originally Posted by BLCMy warranty was already gone when I tried overvolting about a month ago :D. I still can't achieve much over 850MHz though... My power supply is a lot better than the last one I tried, but I still can't rule out the possibility that it might be struggling under load. The test points now read ~4.8v/4.9v, as opposed to ~4.6v with my last power supply, but that was measured at idle; I'll have to test it under load, I guess. I'll give this new firmware a shot first though. 1GHz is the goal, but if I can get to 900MHz stable then I'll be happy!

Not quite; read the comment thread in the forums ;)

The only issues I've had with 1080p h.264 playback have been due to insufficient network bandwidth; in the case of seriously high bitrate stuff, I've had a regular PC fail to play video smoothly when using a 100mbit network adapter. I've not tried really high bitrate stuff on the Pi from a USB source however; most of my HD movies are compressed down to ~15GB, and they play just fine over the network.

The Pi can only use the CPU to decode audio, so anything at 5.1 or over will likely make the Pi struggle, even with an overclock. The solution is audio passthrough.

And bear in mind that it was never designed to be a $35 HTPC; the fact that the GPU can handle 1080p video is purely a bonus.

I have a surround receiver for the audio decoding so that shouldn't be a problem. Though all of my BR rips are uncompressed 40gb *******s.

Originally Posted by PicarroI have a surround receiver for the audio decoding so that shouldn't be a problem. Though all of my BR rips are uncompressed 40gb *******s.

Then that's likely the problem. I'm not sure if that'd play smoothly from USB2, to be honest; not sure if the Pi's implementation is fast enough. It's worth bearing in mind that the Ethernet on the USB bus; I don't think there are any other interface buses on the main core...

My ripped copy of Avatar was exactly the same: just a 40gb file dumped from the disc. I can only play that over a gigabit network, even on a "proper" PC; not even 5GHz 802.11n WiFi can cut it...

There'll be a new release of RaspBMC soon (RC5.0) which will incorporate the new "Turbo" mode. Will be interesting to see how much difference it makes. That's the one thing that bugs me about using the Pi as a media centre: the interface is quite laggy, and you can forget about any other skins bar the default one... XBian seemed faster, but I've since learned (amidst all the GPL kerfuffle) that this is because XBian uses a faster overclock than RaspBMC.